1. Field Methods of Monitoring Atmospheric Systems
Particulate Matter
Copyright © 2006 by DBS

2. Introduction Diameter (μm) Commonly used term < 0.1 fume 0.1-10
Source:
Diameter (μm)
Commonly used term
< 0.1
fume
0.1-10
smoke
10-100
dust
> 100
grit

3. Importance in Atmospheric Chemistry: Reaction and Dispersal
Many atmospheric reactions occur either
In gas/solid phase - on surface of PM
in liquid phase – in water adsorbed onto the surface of particles
e.g. London smog of 1952 PM provided surface for oxidation of SO2
Dispersal mechanism for many pollutants

4. Sources e.g NH4Cl, SO42- / NO3- salts
Mineral dust from weathering of rocks and soils
Natural: forest fires, volcanoes etc.
Man-made: fossil-fuel combustion, industry
Chemical composition can be used to ID source and fate

5. Typical Analysis Total particulate mass concentration
e.g 70 μg m-3 rural
300 μg m-3 urban
10 mg m-3 factory workshop
100 mg m-3 power station flue gases
Chemical Composition
Metals - highly insoluble silicates require dissolution
Inorganic ions
Organics
Size distribution
Total suspended particulate matter (TSP)
As a function of particle size
Very small amounts means an exacting analytical task

6. Question Why is particle size important?
Transport and removal – residence time depends on size
Physiological properties – smaller particles penetrate deeper into lungs
Distribution of chemical species
Effect on atmospheric reactions

7. Sampling Methods A. Filtration and Impaction High-Volume PM10
Dichotomous (divided)
Polyurethane Foam
B. Beta Attenuator Methods (BAM)
C. Tapered Element Oscillating Microbalance (TEOM) Methods
D. Nephelmeter
An advantage of continuous monitoring is that it provides additional information, such as the time of day that peak concentrations occurred

8. A. High-Volume (Hi-Vol) Samplers
Determines mg/m3
Pump up to 90 cfm (~150 m3 h-1)
Draws large volume of air over 24 hr period
Glass fiber or membrane filter
Weighed before and after
0.3 to ~100 μm particle size
Graseby Andersen → Andersen Instruments → Thermo Andersen
Reeve, 2002

9. Question
Convert 90 cfm to m3/min
90 cfm = 90 f3/min
= 90 x (12 in/ft)3 x (2.54 cm/in)3 x (m/100 cm)3
= 90 x … m3/min = 2.55 m3/min
1 cfm = m3/min

10. PM-10 Sampler ‘Add-on’ to standard Hi-Vol sampler
Remove large particles via impaction or settling chambers

11. Filters Choice of filter depends on analyis
Glass fiber – finely spun borosilicate fibers with binder
Cellulose
Membrane - microporous plastic films made from a variety of polymers
Source:
Source:

12. Filters Chose correct filter for analyses Retain correct size
Absence of impurities
Compatible with analytical procedure
Source: Wight, 1994

13. Filters Pros Cons Use Glass FIber - Low water uptake
- High efficiency for particles > 0.3 μm
- Resistant to high T
Organics
Cellulose
- Low head loss
- Low metallic contamination level
- Easily ashed
- Hydrophillic
Metals + inorganic ions
Membrane
- Flat for microscopic analysis
- Hydrophobic
- Chemically resistant
- Large head loss
- Brittle
- Not resistant high T

14. Question
Calculate the PM-10 concentration for the following conditions:
Filter mass gain = mg
Sample time = 1446 min
Initial sampler flow rate = cm3 min-1
Final sampler flow rate = cm3 min-1
Average flow rate = cm/min
Volume of air = cm3/min x 1446 min = 2662 cm3 = x10-3 m3
PM concentration = 6.70 x 10-1 μg / x 10-3 m3 = μg m-3

15. Polyurethane Foam Sampler (PUF)
For organics need both solid and vapor phases
Vapor cartridge is placed in-line with quartz fiber filter for semi-volatile organics
PUF plug
Adsorbent resin (XAD-2)
If vp is high VOC’s may be in aerosol form
Source:
- Pesticides
- PCB’s
- Dioxins
- PAH’s

16. Cascade Impactors Uses adhesion of PM rather than filtration
Flow is constricted, velocity increases
Successively smaller particles adhere to each successive surface
Fractionated according to mass
2.5 – 10 μm / < 2.5 μm
Source:

17. Flow Calibration
Source: Wight, 1994

18. B. Beta Attenuator Methods (BAM)
Beta particles from 14C source are attenuated (lose signal strength) as they pass through particulate deposits on a filter tape
Absorption of radiation is proportional to mass of PM
Contunuous real-time measurement (no weighing required!)
Range: µg/m3
Temperature: -30° to +45°C
New version is heated to remove moisture effects

19. C. Tapered Element Oscillating Microbalance (TEOM) Methods
Air is drawn through a filter at the end of a a tapered oscillating glass tube
Change in frequency is directly related to the mass of PM accumulated
Range: µg/m3
Temperature: -30° to +45°C
Reeve, 2002

20. D. Nephelmeter Optical method
Similar to turbidimeter
Scattering of light by suspended PM, detection by photomultiplier tube. Baffles minimize reflected light

21. Question
There are currently several investigations to compare the results of different PM analyzers. What reasons could contribute to this concern?
Measurements are dependent on atmospheric conditions
Absorbed water may be difficult to control during operations
Meteorological conditions may affect flow rate
Each technique responds differently to individual particle sizes
Some components are volatile and may be lost due to heat (TEOM)

22. MASA: 501
Principle: air is drawn through a 8 x 10” filter at a known flow rate
Mass of particles is determined by the difference in filter mass prior to and after sampling
Concentration of suspended particulate matter is calculated by diving the mass gain of the filter by the volume of air sampled
Lodge, 1988

23. Further Reading
Journal articles

24. Text Books
Hesketh, H.D. (1994) Air and Waste Management: A Laboratory/Field Handbook. CRC Press, Florida.
Lodge, J.P.A. ed. (1988) Methods of Air Sampling and Analysis, 3rd Edition. CRC Press, Florida.
Wight, G.D. (1994) Fundamentals of Air Sampling. CRC Press, Florida.
Winegar, E.D. and Keith, L.A. eds. (1993) Sampling and Analysis of Airborne Pollutants. CRC Press, Florida.